1. Field of the Invention
The present invention relates generally to apparatus for recording/reproducing signals on recording media such as magnetic tapes in a digital manner, and more particularly, magnetic recorder/reproducer for digitally recording image on a digital audio tape and reproducing the same.
2. Description of the Related Art
A magnetic tape recorder/reproducer which is widely known is called a DAT (Digital Audio Tape recording and reproducing apparatus) for and is used converting audio signals into digital signals to record/reproduce the converted signals on a magnetic tape. Through the use of digital signals, the DAT is capable of duplicating the audio signals repeatedly without deterioration in sound quality.
In addition, the DAT generally employs an error correcting code in recording/reproducing a digital signal. As a result, original sound can be reproduced with high fidelity. Even if a part of the information drops out due to defects of the tape or the like, so that the information can not be corrected by the error correcting code, the dropped out signal can be digitally compensated for. Accordingly, the DAT is capable of reproducing an audio signal with an extremely little noise.
Such a magnetic tape recording and reproducing apparatus has operation modes such as a 2 channel mode and a 4 channel mode corresponding to audio signals to be recorded. In the 2 channel mode, there on a magnetic tape are individually recorded two types of audio signals to be converted into sound by two speakers located at a left forward side and a right forward side of the audience. In the 4 channel modes, recorded individually on the magnetic tape are four types of signals which correspond to 4 speakers located at a left forward, a right forward, a left backward and a right backward sides of the audience, respectively.
In recent years, techniques have been developed for recording not only audio but also video signals by a magnetic tape recording and reproducing apparatus.
The present invention relates to a technique for recording/reproducing, as well as audio signals, video signals representing image in such a magnetic recording and reproducing apparatus. FIG. 1 shows a portion for reproducing video signals representing a still image of a magnetic recording/reproducing apparatus directed to such technique.
Referring to FIG. 1, the illustrated magnetic recording and reproducing apparatus having a still image reproducing system employs 4 channel mode as an operation mode. A recording system (not shown) of the apparatus records digital data of one frame of a video signal on the first to fourth recording tracks T1-T4 of a magnetic tape 1 shown in FIG. 3.
Referring to FIG. 2, a dotted line 17 indicates a scanning line of a first field in an image frame 16. Video signals in the first field are sampled at 256 sampling points (1), (2), (3) . . . (256). The first 128 sampled data (data S1-S128 at the sampling points (1)-(128)) is recorded on the first recording track T1. The subsequent 128 data (data S129-S256 at the sampling points (129)-(256)) is recorded on the second recording track T2.
Similarly, video signals on a scanning line of a second field indicated by a solid line 18 are sampled at the sampling points (257)-(512). Referring to FIG. 3 sampling data S257-S384 of the first half of these sampling data is recorded on the third recording track T3 and sampling data S385-S512 in the latter half thereof is recorded on the fourth recording track T4.
The recorded still image is reproduced in a still image reproducing system shown in FIG. 1. Referring to FIG. 1, the still image reproducing system includes a rotary drum 3 having two magnetic heads 14 and 15, reproduced signal processing circuit 2 connected to the magnetic heads 14 and 15, a switch 3 for selectively outputting an output of the reproduced signal processing circuit 2 to either of two terminals 42 and 43, an oscillation circuit 5, switches 6 and 7 connected to the oscillation circuit 5 and the reproduced signal processing circuit 2, a first image memory 28 connected to an output of the switch 6 and the output terminal 42 of the switch 3, a second image memory 29 connected to an output of the switch 7 and the output terminal 43 of the switch 3, a switch 10 having input terminals 51 and 52 connected to outputs of the image memories 28 and 29, respectively, a D/A (digital-to-analog) converter 11 connected to an output of the switch 10, a control portion 24 connected to the reproduced signal processing circuit 2 and the switches 3, 6, 7 and 10, for controlling the respective switches 3, 6, 7 and 10.
The rotary drum 13 rotates, contacts the magnetic tape 1 travelling in a direction indicated by an arrow D1, and scans the magnetic tape by the magnetic heads 14 and 15. The magnetic heads 14 and 15 in turn scan the magnetic tape and reproduce signals on the successive tracks and supplies the same to the reproduced signal processing circuit 2.
The reproduced signal processing circuit 2 is for demodulating signals outputted from the magnetic heads 14 and 15, subjecting the demodulated signals to an error correcting processing, thereby supplying the corrected signal as reproduced signals d1 to an input terminal 41 of the switch 3, and outputting to the control portion 24 a flag signal FL1 indicating completion of a signal reading. In case the input signal is found to be defective, the circuit 2 applies an error flag EFL to the control portion 24. The reproduced signal processing circuit 2 also serves to output a first clock CK1 for determining a timing for signal processing.
The control portion 24, in response to the flag signal FL1, supplies a control pulse SW1 to the switches 3 and 6, a control pulse SW2 which is complementary to the control pulse SW1 to the switches 7 and 10 respectively, thereby controlling an operation of the entire still image reproducing system.
The oscillation circuit 5 has a frequency smaller than that of the first clock CK1 and outputs a second clock CK2 for determining an operation of the reproducing system.
The switch 3 has the input terminal 41 connected to the output of the reproduced signal processing circuit 2 and the output terminals 42 and 43 selectively connected to the input terminal 41 in response to the control pulse SW1. The terminals 42 and 43 are connected to the image memories 28 and 29, respectively. The switch 3 supplies the reproduced signal d1 as a signal d2 to the image memory 28 when the control pulse SW1 is at the high level and in other cases, supplies the reproduced signal d1 as a signal d3 to the image memory 29.
The switch 6 includes an input terminal 61 for receiving the first clock CK1, an input terminal 62 for receiving the second clock CK2 and an output terminal 63 selectively connected to the input terminals 61 and 62 in response to the control pulse SW1. The terminal 63 is connected to the image memory 28. The switch 6 supplies the first clock CK1 when the control pulse SW1 is at the high level, and in other cases, supplies the second clock CK2 as a clock CK3 to the image memory 28.
The switch 7 includes an input terminal 71 for receiving the first clock CK1, an input terminal 72 for receiving the second clock CK2 and an output terminal 73 selectively connected to the terminals 71 and 72 in response to the control pulse SW2. The terminal 73 is connected to the image memory 29. The switch 7 supplies the first clock CK1 when the control pulse SW2 is at the high level, and in other cases, supplies the second clock CK2 as a clock CK4 in to the image memory 29.
When the clock CK3 supplied from the switch 6 is the clock CK1, the image memory 28 stores the reproduced signal d2 applied from the switch 3, in synchronization with the clock CK1, and in other cases, outputs the stored contents as a signal d4 to the switch 10, in synchronization with the clock CK2.
When the clock CK4 supplied from the switch 7 is the clock CK1, the image memory 29 stores the reproduced signal d3 applied from the switch 3, in synchronization with the clock CK1, and in other cases, outputs stored contents as a signal d5 to the switch 10, in synchronization with the clock CK2.
The switch 10 includes the input terminals 51 and 52 connected to the outputs of the image memories 28 and 29, respectively, and an output terminal 53 selectively connected to the input terminals 51 and 52 in response to the control pulse SW2. The output terminal 53 is connected to the D/A converter 11. The switch 10 outputs the output signal d4 of the image memory 28 when the control pulse SW2 is at the low level and in other cases, outputs the output signal d5 of the image memory 29 as a reproduced signal d6, to the D/A converter 11.
The D/A converter 11 converts the digital reproduced signal d6 applied from the switch 10 into an analog signal and outputs a video signal.
Referring to FIGS. 1 to 3, a reproducing system of the conventional magnetic recording and reproducing apparatus operates as follows.
The signals of the two tracks (one field) read out by the magnetic heads 14 and 15 are inputted to the reproduced signal processing circuit 2. The reproduced signal processing circuit 2 demodulates signals and corrects errors by parity or the like. The reproduced signal processing circuit 2 applies the flag FL1 to the control portion 24 when the processing of one field is finished. The reproduced signal processing circuit 2 also applies the digital signal d1 which has been subjected to the above-described signal processing to the input terminal 41 of the switch 3.
The control portion 24 inverts the control pulses SW1 and SW2 every time the flag signal FL1 is inputted thereto. Description will be given in the following of a case where the control pulses SW1 and SW2 are at a high level and a low level respectively. The switch 3 connects the terminals 41 and 42. The switch 6 connects the terminals 61 and 63. The switch 7 connects the terminals 72 and 73. The switch 10 connects the terminals 52 and 53.
The digital signal d1 provided to the output terminal 42 is recorded as the signal d2 in the image memory 28 as the signal d2. On this occasion, the image memory 28 operates in synchronization with the clock CK1 applied from the reproduced signal processing circuit 2.
On this occasion, a clock CK4 applied to the image memory 29 from the switch 7 is the clock CK2 outputted by the oscillation circuit 5. The image memory 29 outputs the stored contents, that is, the image signal d5 recorded one field before, to the input terminal 52 of the switch 10 in synchronization with the clock CK2. Since the switch 10 connects the terminals 52 and 53, the reproduced signal d5 is applied from the output terminal 53 to the D/A converter 11 as the reproduced signal d6. The D/A converter 11 converts the applied digital reproduced signal d6 into an analog signal and outputs the same as a video signal.
After processing one field of the signals, the recorded signal processing circuit 2 again causes the flag signal FL1 to attain the low level, while the control pulses SW1 and SW2 are maintained at the original values. Since the clock CK2 has a frequency smaller than that of the clock CK1, reading of the reproduced signal d5 from the image memory 29 takes time longer than that required for processing one field of signals by the reproduced signal processing circuit 2.
Subsequently, the recorded signals in the subsequent two tracks are sequentially read out by the magnetic heads 14 and 15 and applied to the reproduced signal processing circuit 2. The reproduced signal processing circuit 2 performs the same signal processing as described above, outputs a reproduced signal to the switch 3 and causes the flag FL1 to attain the high level again. The control portion 24 inverts the values of the control pulses SW1 and SW2 in response to the flag FL1 attaining the high level. On this occasion, the switch 3 connects the terminals 41 and 43. The switch 6 connects the terminals 62 and 63. The switch 7 connects the terminals 71 and 73. The switch 10 connects the terminals 51 and 53. Accordingly, on this occasion, the reproduced signal d1 is stored in the image memory 29 through the switch 3. The image memory 28, in synchronization with the clock CK2 applied from the oscillation circuit 5, outputs the stored contents as a reproduced signal d4. The reproduced signal d4 is applied as the reproduced signal d6 to the D/A converter 11 through the switch 10. The D/A converter 11 converts the applied digital reproduced signal d6 into an analog signal and outputs the same as a video signal.
When writing of the reproduced signal into the image memory 29 and outputting the reproduced signal d4 from the image memory 28 are finished, the reproduced signal processing circuit 2 has already caused the flag signal FL1 to return to the low level. Finishing the signal processing of the subsequent track and starting to output the processed signals to the switch 3, the reproduced signal processing circuit 2 once again causes the flag FL1 to return to the high level. The control portion 24 again inverts control pulses SW1 and SW2 in response to the change of the flag FL1. As a result, the image memory 28 starts to store the reproduced signal again and the image memory 29 starts to output the stored contents.
As described above, one field of the outputs of the image memories 28 and that of the image memory 29 are alternately applied to the D/A converter 11. Accordingly, the image recorded on the magnetic tape 1 can be displayed by a display apparatus such as a CRT (Cathode-Ray Tube).
The DAT is capable of recording and reproducing not only audio signals but also video signals as described above. The DAT can be used in an extremely wide field. In addition, since the DAT is capable of recording information on a tape in a digital manner, a so-called "search mode" can be provided. In the search mode, recorded contents in a recording portion can be directly located and reproduced by designating a particular position of the tape and fast forwarding the tape to the designated position. As a result, desired information can be obtained quickly. Therefore, the DAT can be used in an extremely wide field not limited to recording of music.
However, in the above-described conventional magnetic recording and reproducing apparatus, a long search time is required in a search mode. In a conventional apparatus, about five seconds is required for outputting one frame of image data. Five seconds are considered to be a very long time especially for a person who wants to obtain specific information rapidly. Therefore, it is impossible to make full use of the advantage in the search mode.